Control system for electric valves



Feb. 21, 1950 E. SCHORNO CONTROL SYSTEM FOR ELECTRIC VALVES 2Sheets-Sheet 1 Filed Feb. 10, 1947 Feb. 21, 1950' E. scHoRNo 2,498,457

CONTROL SYSTEM FOR ELECTRIC VALVES Filed Feb. 10, 1947 2 Sheets-Sheet 22 Ill IIIIIIII 18 Patented Feb. 21, 1950 CONTROL SYSTEM FOR ELECTRICVALVES Eduard Schorno, Zurich, Switzerland, assignor to MaschinenfabrikOerlikon,

Zurich-Oerlikon,

Switzerland, a Swiss firm Application February 10, 1947, Serial No.727,612 In Switzerland February 12, 1946 Claims.

The present invention relates to a control sys tem for electric valvesand particularly to a grid extinguishing system to prevent arc-backs andoverload currents.

Up to the present known devices or arrangements designed for theprevention of overload current or arc-backs in electric valves do notprevent the formation of an arc-back but are merely concerned in puttingout or extinguishing such an are after its formation, using for thispurpose grid action which is initiated only after the occurrence of thisphenomenon called arcback. This grid action is usually designed torespond to currents and voltages supplied by the alternating current ordirect current network of the rectifier. Whenever an arc-back occurs therectifier, the rectifier-transformer and the associated equipment issubjected to heavy overload stresses and the so stricken elements sufferoften serious damages.

The main purpose of the present invention is therefore to provide asuitable system to prevent the arc-back phenomenon by extinguishing thenormal are or blocking of the anodes by grid action before the arc-backphenomenon takes place. The coordination of the necessary elements toachieve this is referred to as grid extinguishing system and accordingto this invention said grid extinguishing system actuated by fractionalvoltages of the normal arc voltage. In this respect it has beenestablished that the voltage fluctuations of said are furnishes acriterium for the arc-back phenomenon and that its occurrence isinvariably due to eXcess voltage of certain magnitude of the normal arc.

Other features will be apparent from the detailed description of acontrol system, incident to the present invention, described hereafterin conjunction with the accompanying drawing in which is:

Figure 1 a control system for a mercury arc rectifier in which the arcvoltage between the vessel and the cathode is used to actuate the gridextinguishing system of the faulty working anode, in order to preventarc-back.

Figure 2 shows the application of a glow tube in a system accordingFigure 1.

Figure 3 shows the application of gas type discharge tubes, incidentalto the behavior of the normal are, characterized by the occurrence ofexcess voltages before a back-arc is initiated, as noted above.

Referring to Figure 1-showing diagrammatically a system of fewinexpensive elementsl indicates the rectifier-transformer, 2 therectifier I ure of the normal arc voltage.

vessel, 3 the anodes, 4 the grids, 5 an anode housing, 6 the cathode, 1the arc, 8 the grid-resistors, 9 a quick acting relay, In an auxiliaryrectifier, II a relay, l2 a battery, I3 alternating current net workterminals of approximately 220 volts and M a switch; l5 indicates theholding coil of the quick acting relay 9.

In a rectifier working at full load arc-backs are apt to develop, whenchanges in the degree of vacuum, respectively changes in the pressure ofthe mercury vapor occur or in cases of heavily increased load current.Under such conditions the arc voltage increases, to such a value in thecircuit arrangement shown that the quick acting relay 9, controlled bythe voltage drop between the vessel and cathode, is actuated, therebyconnecting all grids 4 with the negative terminal of the battery [2,blocking thereby the rectifier operation before arc-backs can occur. Thepotential between the vessel and cathode is a meas- It is also apparentthat it is possible to select an operating coil for the quick actingrelay 9 which will be operable on an overload current of the rectifier.In order to prevent relay 9 to return immediately to its operatingposition after its blocking operation, the armature of relay 9 is causedto remain attracted by means of the holding coil I5, which is fed fromthe rectifier l0. At the instant the relay 9 functions the rectifier I0is supplied with A. C. current, in that the armature of relay H fallsoff and connects two contacts, thereby closing the supply circuit of therectifier I0. By opening and reclosing the switch 14 in the outputcircuit of the rectifier ID the grid blocking action of the relay 9 canbe made inoperative. When the circuit of the holding coil [5 isinterrupted and the quick acting relay 9 is reset by means of a spring,the entire rectifier system resumes its normal operating position andthe control system is again ready to protect the rectifier against theback-arc phenomenon.

In the modified system according Figure 2 the quick acting relay 9 isconnected to an auxiliary electrode 21, provided for each anode 3, overthe intermediary of a glow tube [6. Thus the voltage between theauxiliary electrode and the oathode is employed as a measure for the arcvoltage. The glow tube IB is rated to respond to a voltage adapted tothe type of rectifier to be protected, operating the quick acting relay9 whenever it is necessary to protect the rectifier against the back-arcphenomenon initiated by over voltage or overload current.

It will be apparent that other fractional voltages of the normal arcvoltage such as gridcathode, grid-vessel, grid to grid and anode to gridmay also be used to actuate the grid extinguishing system. In the systemaccording to Figure 2 vacuum tubes may be used replacing the glow tubeor for direct feeding of the holding coil t5 of the quick acting relay9-. Damaged parts of the rectifier or unclean vessels may promoteback-arcs.

In a properly built rectifier or valve when. working under normalcondition at its rated load, back-arc occurs only seldom. However underoverload especially when said overload is main tained over a long periodof time, back-arcs are apt to become a common occurrence. 1

Tests and careful watching of the behavior during operation have shownthat back-arcs always occur during the time of zero current passage andparticularly immediately after the interruption of the normal. arc. Itappears to be characteristic for this behavior that shortly be forearc-backs, toward the end of the current pulse, the normal arc voltagebetween anode and cathode increases to a magnitude equal to severaltimes the value of the normal arc voltage. The; modifications of thesystem shown in Figure 3 therefore comprises means whereby only" thefaulty operating anode is extinguished by its associated gridextinguishing system. By this, normal operation or" the rectifier, whilethe protective device is actuated, is not interrupted.-

Referring to Figure '3, the numerals it, wand t9 indicate resistors,Eare time delay relays, 21 are signalling relays and 22 are gas typedischarge tubes; 23 indicate m'eans to provide for grid control voltage.Assumingthat' the rectifier operates under overload and that at one ofthe anodes abnormal high peak voltages towards the end of a currentpulse occur, then the modified system operates as described hereafter.The arrangement comprises an auxiliary electrode 4 designed to serve asvoltage tap which is connected with the grid of the gas type tube 22'over an intermediate limiting resistor [9. The tube 22 under theassumedcondition will begin to glow closing thereby the circuit oversaid tube- 22;,grid battery i2 and resistors i? energizing the uppergrid 3, in relation to the cathode 6, by a negative potential, wherebythe particular anode 3 is blocked. Operationcf the other anodes of therectifier is thereby not-interrupted and merely a slight drop in theoutput voltage will be noticed, The time relay 2c is designed toput theparticular anode 3- after a predetermined time back in operation again,thereby compensating said previous voltage loss. The normal operation ofthe rectifier is hardly affected while the protective equipment of themodified system functions to prevent the back-arc phenomenon; Itisunderstood that handoperated means may also be used to block the faultyanode. The

signalling relay 2 operating ele'ctromagnetically or by photoelectriccells, in well" known manner, is designed to indicatethe'iau-ltyoperating a'n'ode'l.

In caseswhere the signalling of the faulty" anode or uninterruptedoperation-in View of only short interruptions is of no necessity thesystem may be further modified inthat but one.

What I claim is:

1. In combination with an electric valve means comprising at least oneanode, a cathode and a control grid, means forming a grid extinguishingsystem and including a relay, circuit means for directly energizing saidrelay by a fraction of the arc voltage, a normally open circuitcontaining a source of direct current having its positive terminalconnected with said cathode, and means operated by said relay when saidfraction of said are voltage exceeds a predetermined value tocondu'ctively connect said control grid with the negative terminal ofsaid direct current circuit, whereby said grid extinguishing systembecomes operative to block the anode associated with saidv grid.

2. In combination with an electric valve means comprising at least oneanode, a cathode and a control grid, means forming a grid extinguishingsystem and including a relay, circuit means for directly energizing.relay by a fraction 01? the voltage drop between said anode and saidcathode, a normally open circuit containing'a source of direct currenthaving its positiveuterm-inal connected with said cathode, andmeansoperated by said relay when said fraction of said voltage drop exceeds apredetermined value to con ductiveiy connect said control grid with thenegative terminal of said direct current circuit,"

system and including azre'layhavinga normally deenergized holding coil,circuit'me'ans for directly energizing said relay by the Voltage dropbetween said auxiliary electrode and said cath ode, a normally opencircuit containing'a source of direct current having its positiveterr'ninalc connected with said cathode, and means operated by saidrelay when said voltage drop exceeds a predetermined value toconductively connect said control grid with the negative terminalofxs'aid direct current circuit and to cause en'ergizati'on of saidholding coil, whereby said grid extinguishing system becomes operativetoblo'ck the anode associated with said grid and manually operable meansto cause deenergizat-ion of said holding coil and a disconnection ofsaid control grid from said negative terminal.

e. In combination with an electric'valve means:

comprising at least one anode, a cathodaa con trol grid and an auxiliaryelectrode arranged in a vessel, means forming a grid extinguishingsystem and including a relay, circuit means irrcludin a glow tubefordirectly energizing said relay by the voltage drop between saidauxiliary electrode and said cathode, a normally open circuit containinga source of direct current having its positive terminal connected withsaid oathode, and means operated by said clay when said voltage dropexceeds a predetconductively connect said control grid with the negativeterminal of said direct current circuit, whereby said grid extinguishingsystem becomes operative to block the anodeas'sociate'd with said grid.

5. Incornbination with an electric valve means comprising at least oneanode, a cathode and a control grid arranged in a vessel-means formingagrid extinguishing system and including a relay having a movablearmature a :no-rdined value to mally deenergized holding coil, circuitmeans for directly energizing said relay by the voltage drop betweensaid vessel and said cathode, a normally open circuit containing asource of direct current having its positive terminal connected withsaid cathode, and means operated by the movable armature of said relaywhen said voltage drop exceeds a predetermined value to conductivelyconnect said control grid with the negative terminal of said directcurrent circuit and to cause energization of said holding coil, wherebysaid grid extinguishing system becomes operative to block the anodeassociated with said grid and manually operable means to causedeenergization of said holding coil and a disconnection of said controlgrid from said negative terminal.

6. In combination with an electric valv means comprising at least oneanode, a cathode, a control grid and an auxiliary electrode arranged ina vessel, means forming a grid extinguishing system and including arelay, circuit means including a gas discharge valve for energizing saidrelay by the voltage drop between said auxiliary electrode and saidcathode, a normally open circuit containing a source of direct currenthaving its positive terminal connected with said cathode, and meansoperated by said relay when said voltage drop exceeds a predeterminedvalue to conductively connect said control grid with the negativeterminal of said direct current circuit, whereby said grid extinguishingsystem becomes operative to block the anode associated with said id.

7. In combination with an electric valve means comprising at least oneanode, a cathode, a control grid and an auxiliary electrode arranged ina vessel, means forming a grid extinguishing system and including arelay, circuit means including a signalling relay for energizing saidrelay by the voltage drop between said auxiliary electrode and saidcathode, a normally open circuit containing a source of direct currenthaving its positive terminal connected with said cathode, and meansoperated by said relay when said voltage drop exceeds a predeterminedvalue to conductively connect said control grid with the negativeterminal of said direct current circuit, whereby said grid extinguishingsystem becomes operative to block the anode associated with said grid.

8. In combination with an electric valve means comprising at least oneanode, a cathode, a control grid and an auxiliary electrode arranged ina vessel, means forming a grid extinguishing system and including arelay, circuit means including a gas discharge valve and a signallingrelay for energizing said relay by the voltage drop between saidauxiliary electrode and said cathode, a normally open circuit containinga source of direct current having its positive terminal connected withsaid cathode, and means operated by said relay when said voltage dropexceeds a predetermined value to conductively connect said control gridwith the negative terminal of said direct current circuit, whereby saidgrid extinguishing system becomes operative to block the anodeassociated with said grid.

9. In combination with an electric valv means comprising a plurality ofanodes, a cathode, a control grid for each anode and an auxiliaryelectrode for each anode, means forming a grid extinguishing system andincluding a plurality of relays, one for each anode, circuit means foreach said relays for energizing said relays by the voltage drop betweenthe auxiliary electrode of their associated anode and said cathode, anormally open circuit containing a source of direct current having itspositive terminal connected with said cathode, and means operated byeach of said relays when the voltage supplied to the same exceeds apredetermined value to conductively connect the control grid associatedwith the respective auxiliary electrode with the negative terminal ofsaid source of direct current, whereby the grid extinguishing systembecomes operative to block solely th anode associated with said controlgrid, the other anodes remaining in operative condition.

' 10. In combination with an electric valve means comprising at leastone anode, a cathode and acontrol grid, means forming a gridextinguishing system and including a relay, circuit means for energizingsaid relay by a fraction of the arc voltage, a normally open circuitcontaining a source of direct current having its positive terminalconnected with said cathode, means operated by said relay when saidfraction of said are voltage exceeds a predetermined value toconductively connect said control grid with the negative terminal ofsaid direct current circuit, whereby said grid extinguishing systembecomes operative to block the anode associated with said grid, aholding coil operatively connected with said relay, a second circuitmeans adapted to be automatically closed when said relay is renderedoperative to energize said holding coil and thereby holding said relayin its grid extinguishing position, and manually operable switch meansin said second circuit means for opening the latter and causingdeenergisation of said holding coil.

EDUARD SCI-IORNO.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

